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Enabling High-Apogee Science Missions for Launch on Low-Cost Pegasus Launch Vehicles, 15-9456

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Principal Investigators
David J. McComas
John R. Scherrer

Inclusive Dates:  01/12/04 - 07/01/04

Background - This internal research project involved examining the trade space associated with developing the baseline design of a small spacecraft to a high-apogee orbit using a low-cost Pegasus launch vehicle. Several factors have emerged during the past few decades that have increased the need for high-apogee science missions that are launched on the low-cost Pegasus launch vehicle.

  • There is a recent push for missions with high apogees (more than 5 RE) to maximize science return as well as to pursue new scientific objectives not attainable from low earth orbit.
  • NASA's science budget is flat, increasing the need for low-cost missions; by decreasing the launch vehicle cost, the total mission cost can drop significantly. Currently, the lowest cost United States-built launch vehicle is the Pegasus.
  • Foreign launch vehicles are typically cheaper and provide increased performance, but they are ground-ruled out for almost all NASA missions because government funding cannot be used to purchase foreign launch services.

The goal of this project was to investigate trades to enable the implementation of low-cost, high-apogee missions and to develop a point design for a high-altitude mission based on placing a ~100-kilogram spacecraft into a ~35 RE (~220,000-kilometer) apogee orbit.

Approach - The SwRI project team worked multiple trade studies in close collaboration with the Orbital Science Corporation (OSC), an established provider of low-mass NASA space science satellites and the provider of the Pegasus launch system, to ensure that the trade studies were thorough and the resulting design could be implemented. Trade studies included looking at methods to minimize the required mass of the spacecraft and payload to reduce the Pegasus launch mass. Likewise, the project developed a concept for adding a kick motor fourth stage to the Pegasus to enhance its lift capability. In general, SwRI was the lead of the overall study, the lead on payload and payload accommodation issues, and led the definition of spacecraft and mission requirements studied by OSC. We also held several peer reviews, some of which included outside consultants, to verify that our design approach was viable and sound.

Accomplishments - A primary product of the proposed work was to develop a point design for a high-altitude mission. For this purpose, we baselined the Interstellar Boundary Explorer (IBEX) mission, which requires placing a ~100-kilogram spacecraft and payload into a ~37 RE (~235,986-kilometer) apogee orbit. This spacecraft/payload size is large enough to deliver good science return for many types of missions and the 37 RE orbit extends well outside the magnetosphere and beyond the bow shock, enabling such missions to study much of the magnetosphere, the magnetosheath, the solar wind, as well as doing remote sensing from well outside the Earth's high background environment. The final product of this project was the IBEX Concept Study Report recently submitted and presented to NASA that thoroughly documents the IBEX baseline point design.

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